Trochoidal machines (the term “trochoidal” as used herein is also intended to encompass epitrochoidal machines as well as true trochoidal ones) have long been known. Perhaps the most well known example is the Wankel engine. Such machines have, however, been used for other purposes, including, for example, the compression of gas. As is well known, such rotary machines include a rotor that is nominally triangular in shape and which generally has the appearance of an equilateral triangle whose three sides are convex. The rotor is mounted on an eccentric on the machine shaft and typically is tied to a housing by means of a spur gear configuration on one side of the rotor meshed with a ring gear formation on the corresponding side of the machine housing.
The rotor is contained in a chamber that is trochoidal in shape. Seals are carried at each apex of the rotor to sealingly engage the chamber periphery. Side seals are also carried by the rotor near its periphery for sealingly engaging the sides of the chamber and typically, so-called corner seals are located at the interface of the ends of the apex seals and the ends of the side seals on both sides of the rotor. Intake and exhaust porting is provided in the chamber periphery with one port being located on one side of the so-called “waist” of the chamber and the exhaust port on the other.
Oppositely of the porting, other components may be located, depending upon the use to which the machine is being put. In the case of an engine, ignition devices are located of one or both sides of the waist oppositely of the ports. Alternatively, fuel injection devices may be located in generally the same place as the ignition devices if the engine is to operate on the diesel cycle.
While engines of this sort have been commercially produced, particularly for powering vehicles, they have not achieved the acceptance of conventional reciprocating engines for a variety of reasons.
Specifically, a known type of a rotary engine that has been commercially sold as a power plant for a vehicle has a theoretical compression ratio of 10:1 but only produces a maximum internal pressure in the range of 85 to 100 psi. during the compression part of the rotary cycle at cranking speed. On the other hand, a reciprocating engine having the same compression ratio would, at cranking speed, produce an internal pressure in the range of 170 to 200 psi., and if the seals of either engine were perfect, the internal pressure would be significantly higher. The difference between the theoretical and actual pressures is the result of seal leakage. Seal leakage is more critical in a rotary engine than in a reciprocating engine because at 6000 rpm, a reciprocating engine's compression phase takes approximately 0.005 seconds, whereas that of the rotary engine takes approximately 0.0075 seconds. The seals of the rotary engine are therefore subject to leakage for a 50% longer period of time than those of reciprocating engines at the same rpm.
Because rotary engines can and do operate at significantly higher rpms, the problem is somewhat lessened. However, due to the lesser compression attainable in rotary engines, the same are currently inferior to reciprocating engines in terms of power produced per unit of fuel, which translates into a reduction in gas milage, and increased hydrocarbon admissions. Thus, rotary engine performance is far inferior to its potential.
Apex seals are perhaps the greatest cause of lack of compression due to leakage in a rotary engine of the type having a rotor provided with apexes. Specifically, internal combustion engines of all types typically rely on so-called “gas energization” of seals to produce the desired sealing effect during compression and combustion phases of their cycle of operation. Seals that are gas-energized are typically found somewhat loosely in grooves in which they may move slightly from side to side and in and out of the groove. Conventionally, a light biasing spring will be placed between the bottom of the groove and the innermost end of the seal to bias the opposite end of the seal into light sealing contact with the operating chamber wall. When subject to pressure, as during compression or combustion phases of the operating cycle, the pressure acts against the high pressure side of the seal to force the opposite side to seal tightly against the side of the groove. The gas under pressure also enters the groove to act against the radially inner end of the seal and bias the same outwardly into good sealing engagement with the wall of the operating chamber. This is true whether the seal is a piston ring, an apex seal, or a side seal. There is, however, a major difference in the operation of apex seals. During the compression phase of an engine, the apex seal must seal against the trailing wall of the seal receiving groove to achieve compression. When the compression phase is completed, and the combustion phase is entered, the higher pressure now exists on the opposite side of the apex seal, requiring it to shift within its groove so that its leading side seals against the leading side of the seal receiving groove. This shifting of the apex seal leads to the momentary creation of a leakage path around the seal between the sides of the groove as the seal transitions from sealing engagement against one groove wall to sealing engagement against the other groove wall. Moreover, when the pressure acting against the leading face and inward end of the seal, acts against the outermost end of the seal and the trailing face may reach a value so that there is a net positive pressure acting on the seal in the radially inward direction. It can be sufficient to exceed the combined force of the biasing spring and centrifugal force generated by the mass of the apex seal. Consequently, a small gap may occur at the interface of the outermost tip of the seal and the wall of the operating chamber, allowing leakage through this gap as well. All of this creates a loss of efficiency.
A second point of failure of apex seals can occur when the pressure from combustion increases very rapidly. In order to maintain a tight seal between the outer sealing edge of the apex seal and the operating chamber wall, the pressure at the inner part of the apex seal must also increase substantially equally as rapidly. However, since the gas to create the pressure must travel through a narrow gap between the apex seal and the side of the groove in which the seal resides, the outward biasing pressure cannot increase as rapidly and an inwardly movement of the seal results in a loss of sealing contact, especially at high rpm.
A third cause of leakage can occur as an apex seal passes 300° past bottom dead center (bdc) to the time it reaches the exhaust port, typically located at about 60° past bdc. During this time, pressure in the trailing chamber is required to hold the apex seal tight against the leading face of the groove in which it resides. However, frictional forces at the tip of the apex seal act counter to the pressure forces and at some point in time between 300° and 60° past bdc, a gap will occur on both sides of the apex seal resulting in undesirable leakage around the apex seal.
Still another cause of loss of pressure occurs as the apex seal passes recesses in the operating chamber wall employed in ignition and/or fuel injection systems.
A further cause may result from seal warpage. Extreme heat encountered in the operating cycle of the engine may cause a conventional apex seal to warp out to in or from side to side resulting in the creation of more leakage paths at the tip of the seal.
Still another cause of leakage may result if the seal resonates at its natural frequency along its length. Because the slot in which the seals are received are larger than the seal, i.e., the slot width is greater than the width of the seal, the seal may resonate, creating gaps which allow leakage.
The present invention is directed to overcoming one or more of the above problems.